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- .. _seats:
- ==============================================================================
- Seats
- ==============================================================================
- Each device in libinput is assigned to one seat.
- A seat has two identifiers, the physical name and the logical name. The
- physical name is summarized as the list of devices a process on the same
- physical seat has access to. The logical seat name is the seat name for a
- logical group of devices. A compositor may use that to create additional
- seats as independent device sets. Alternatively, a compositor may limit
- itself to a single logical seat, leaving a second compositor to manage
- devices on the other logical seats.
- .. _seats_overview:
- ------------------------------------------------------------------------------
- Overview
- ------------------------------------------------------------------------------
- Below is an illustration of how physical seats and logical seats interact:
- .. graphviz:: seats-sketch.gv
- The devices "Foo", "Bar" and "Spam" share the same physical seat and are
- thus available in the same libinput context. Only "Foo" and "Bar" share the
- same logical seat. The device "Egg" is not available in the libinput context
- associated with the physical seat 0.
- The above graph is for illustration purposes only. In libinput, a struct
- **libinput_seat** comprises both physical seat and logical seat. From a
- caller's point-of-view the above device layout is presented as:
- .. graphviz:: seats-sketch-libinput.gv
- Thus, devices "Foo" and "Bar" both reference the same struct
- **libinput_seat**, all other devices reference their own respective seats.
- .. _seats_and_features:
- ------------------------------------------------------------------------------
- The effect of seat assignment
- ------------------------------------------------------------------------------
- A logical seat is interpreted as a group of devices that usually belong to a
- single user that interacts with a computer. Thus, the devices are
- semantically related. This means for devices within the same logical seat:
- - if the same button is pressed on different devices, the button should only
- be considered logically pressed once.
- - if the same button is released on one device, the button should be
- considered logically down if still down on another device.
- - if two different buttons or keys are pressed on different devices, the
- logical state is that of both buttons/keys down.
- - if a button is pressed on one device and another device moves, this should
- count as dragging.
- - if two touches are down on different devices, the logical state is that of
- two touches down.
- libinput provides functions to aid with the above:
- **libinput_event_pointer_get_seat_button_count()**,
- **libinput_event_keyboard_get_seat_key_count()**, and
- **libinput_event_touch_get_seat_slot()**.
- Internally, libinput counts devices within the same logical seat as related.
- Cross-device features only activate if all required devices are in the same
- logical seat. For example, libinput will only activate the top software
- buttons (see :ref:`t440_support`) if both trackstick and touchpad are assigned
- to the same logical seat.
- .. _changing_seats:
- ------------------------------------------------------------------------------
- Changing seats
- ------------------------------------------------------------------------------
- A device may change the logical seat it is assigned to at runtime with
- **libinput_device_set_seat_logical_name()**. The physical seat is immutable and
- may not be changed.
- Changing the logical seat for a device is equivalent to unplugging the
- device and plugging it back in with the new logical seat. No device state
- carries over across a logical seat change.
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